Rectifiers for AC to DC conversion of high frequency signals have been well known for decades. A particular type of diode rectifier when coupled to an antenna, called a rectenna, has also been known for decades. More specifically, over 20 years ago, Logan described using an array of rectennas to capture and convert microwaves into electrical energy in U.S. Pat. No. 5,043,739 granted Aug. 27, 1991. However, the dimensions of the antenna limited the frequency until recently, when Gritz, in U.S. Pat. No. 7,679,957 granted Mar. 16, 2010, described using a similar structure for converting infrared light into electricity, and Pietro Siciliano suggested that such a structure may be used for sunlight in “Nano-Rectenna For High Efficiency Direct Conversion of Sunlight to Electricity,” by Pietro Siciliano of The Institute for Microelectronics and Microsystems IMM-CNR, Lecce (Italy).
Still, the minimum dimensions required for such visible light rectennas are generally in the tens of nanometers. While these dimensions may be accomplished by today's deep submicron masking technology, such processing is typically far more expensive than the current solar cell processes, which require much larger dimensions.
Still, as Logan pointed out in U.S. Pat. No. 5,043,739, the efficiency of microwave rectennas can be as high as 40%, more than double that of typical single junction poly-silicon solar cell arrays, and when using metal-oxide-metal (MOM) rectifying diodes, as Pietro suggests, no semiconductor transistors are needed in the array core.
As such, it may be advantageous to be able to utilize the existing fine geometry processing capability of current semiconductor fabrication without incurring the cost of such manufacturing.
Also, recently, Rice University reported that their researchers created a carbon nanotube (CNT) thread with metallic-like electrical and thermal properties. Furthermore, carbon nanotube structures are becoming more manufacturable, as described by Rosenberger et al. in U.S. Pat. No. 7,354,977 granted Apr. 8, 2008. Various forms of continuous CNT growth may have also been contemplated, such as Lemaire et. al. repeatedly harvesting a CNT “forest” while it is growing in U.S. Pat. No. 7,744,793 granted Jun. 29, 2010, and/or put into practice using techniques described by Predtechensky et al. in U.S. Pat. No. 8,137,653 granted Mar. 20, 2012. Grigorian et al. describes continuously pushing a carbon gas through a catalyst backed porous membrane to grow CNTs in U.S. Pat. No. 7,431,985 granted Oct. 7, 2008.
Furthermore, others have contemplated using CNTs for various structures such as Rice University's CNT thread as described in “Rice's carbon nanotube fibers outperform copper,” by Mike Williams, posted on Feb. 13, 2014 at: news.rice.edu/2014/02/13/rices-carbon-nanotube-fibers-outperform-copper-2; magnetic data storage as described by Tyson Winarski in U.S. Pat. No. 7,687,160 granted Mar. 30, 2010; and in particular, antenna-based solar cells, as described by Tadashi Ito et al. in US Patent Publication 2010/0244656 published Sep. 30, 2010. Still, Ito et al. did not describe methods to inexpensively construct carbon nanotube solar antennas for efficient conversion of solar energy.